1. Field
The disclosed technology relates to a balancing method of a battery pack and a battery cell balancing system.
2. Description of the Related Technology
In general, a portable electronic device such as a portable laptop computer and a portable machine tool has a battery pack that is capable of being recharged. Each battery cell of the battery pack has a capacity deviation caused by various steps during a manufacturing process. Accordingly, the battery pack generates a deviation for the charge and discharge voltages of each battery cell in charge and discharge cycles. Therefore, in the battery pack, some battery cells may be overcharged during charge, and some battery cell may be over-discharged during discharge. As described above, the overcharge or over-discharge of the battery cells reduces the capacity of the battery pack, deteriorates the battery pack, and decreases the cycle-life of the battery pack.
Accordingly, cell balancing for controlling a voltage difference between battery cells to be in a permissible range or to be the same in a battery pack is important. In a conventional balancing method, a balancing operation is executed if the voltage difference between the cells is generated after charging. However, when using this method, balancing is possible in a short time in a small capacity battery pack, but balancing is impossible within the same short time in a large capacity battery pack. For example, when a voltage difference of 100 mV between the cells is generated in a large capacity battery pack including 50 A cells, if a balancing current of 300-500 mA is used, the balancing must be executed for more than about 10 minutes for the balancing effect. Meanwhile, if the balancing current is increased to reduce the balancing time, power dissipation is not only increased, but also heat is increased in the battery pack and stress is applied to the elements thereof. The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.